Method and apparatus for measuring parameters of a stratified flow

ABSTRACT

Various methods are described for measuring parameters of a stratified flow using at least one spatial array of sensors disposed at different axial locations along the pipe. Each of the sensors provides a signal indicative of unsteady pressure created by coherent structures convecting with the flow. In one aspect, a signal processor determines, from the signals, convection velocities of coherent structures having different length scales. The signal processor then compares the convection velocities to determine a level of stratification of the flow. The level of stratification may be used as part of a calibration procedure to determine the volumetric flow rate of the flow. In another aspect, the level of stratification of the flow is determined by comparing locally measured velocities at the top and bottom of the pipe. The ratio of the velocities near the top and bottom of the pipe correlates to the level of stratification of the flow. Additional sensor arrays may provide a velocity profile for the flow. In another aspect, each of the sensors in the array includes a pair of sensor half-portions disposed on opposing lateral surfaces of the pipe, and the signal processor determines a nominal velocity of the flow within the pipe using the signals.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 60/522,164, (CiDRA Docket No. CC-0732) filed Mar. 10,2004, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

This invention relates to a method and apparatus for measuringparameters such as velocity, level of stratification, and volumetricflow rate of a stratified flow within a pipe.

BACKGROUND

Many industrial fluid flow processes involve the transportation of ahigh mass fraction of high density, solid materials through a pipe. Forexample, a process known as hydrotransport is used in many industries tomove solids from one point to another. In this process, water is addedto the solids and the resulting mixture is pumped through typicallylarge diameter pipes.

Operation of a hydrotransport line typically involves some degree ofstratification, where flow velocity near the bottom of the pipe is lessthan flow velocity near the top of the pipe. The level of stratificationin this flow (i.e., the degree of skew in the velocity profile from thetop of the pipe to the bottom of the pipe) is dependent on numerousmaterial and process parameters, such as flow rate, density, pipe size,particle size, and the like. If the level of stratification extends tothe point where deposition velocity is reached, the solids begin tosettle to the bottom of the pipe, and if the condition is undetected andpersists, complete blockage of the pipe can occur, resulting in highcosts associated with process downtime, clearing of the blockage, andrepair of damaged equipment.

To reduce the chance of costly blockage formation, current practice isto operate the pipeline at a flow velocity significantly above thecritical deposition velocity. However, this technique has twosignificant drawbacks due to operating at higher velocities: it causeshigher energy usage due to higher friction losses, and it causes higherpipe wear due to abrasion between the solids and the pipe inner surface.This technique may also be undesirable to due high water consumption. Areliable means of measuring parameters such as velocity, level ofstratification, and volumetric flow rate of a stratified flow wouldenable operating the pipeline at a lower velocity, resulting in energysavings and lower pipe wear.

Various technologies exist for measuring physical parameters of anindustrial flow process. Such physical parameters may include, forexample, volumetric flow rate, composition, consistency, density, andmass flow rate. While existing technologies may be well-suited foraggressive, large diameter flows, these technologies may be unsuitablefor stratified flows, which can adversely affect accuracy in measuringphysical parameters of the flow.

Several non-commercial techniques for determining the onset of solidsdeposition in slurry pipelines are described in recent literature. Forexample, one technique uses a commercial clamp-on ultrasonic flow meter,in Doppler mode, with coded transmissions and cross-correlationdetection. The detection point for the meter is set at a certain pipelevel, e.g., 10% above the pipe invert (i.e., the pipe bottom forhorizontal pipes). Cross-correlation of a time-gated ultrasonic returnsignal enables detection of reflected signals only from the set point. Adecrease in coherence between transmitted and received signals indicatesunsteady flow conditions due to solids deposition.

Another existing non-commercial technique measures the apparentelectrical resistivity of the slurry near the pipe invert, with a changein resistivity indicating the formation of a solids bed. This techniquewas deemed to be not very successful due to poor repeatablility andother problems.

Another non-commercial technique utilizes self-heating thermal probesmounted in the slurry. A moving slurry removes temperature from theprobes, while a stationary solids bed around the probe causes heat tobuild up. Thus a temperature rise is indicative of solids deposition.While this technique is promising, it is an invasive technique requiringthe thermal probes to be placed in the pipe. Such invasive techniqueshave drawbacks in that they require the process to be stopped to allowfor installation and maintenance of the probes.

Another technique involves the installation of a short pipe withslightly larger inside diameter, where a stationary solids bed isallowed to form and is maintained as a control while the main pipelineis operated with no solids bed. The control solids bed is then monitoredby one or more of the techniques described above. An increase in theheight of the control bed then indicates the likely formation of asliding bed in the main pipeline, which is a precursor of a stationarybed and eventual blockage. When the control solids bed height increasesbeyond a certain limit, the flow rate may be increased to avoid solidsdeposition.

Thus, there remains a need for a method and apparatus for measuringparameters such as velocity, level of stratification, and volumetricflow rate of a stratified flow.

SUMMARY OF THE INVENTION

The above-described and other needs are met by an apparatus and methodof the present invention, wherein a spatial array of sensors is disposedat different axial locations along the pipe. Each of the sensorsprovides a signal indicative of unsteady pressure created by coherentstructures convecting with the flow. A signal processor determines, fromthe signals, convection velocities of coherent structures havingdifferent length scales. The signal processor then compares theconvection velocities to determine a level of stratification of theflow. In one embodiment, the signal processor compares the convectionvelocities by constructing a plot of the convection velocities as afunction of the length scales, and determining a slope of a best-fitline through the plot. The slope of the line indicates the level ofstratification of the flow.

In one embodiment, the slope is used as part of a calibration procedureto determine the volumetric flow rate of the flow. For example, thecalibration may include determining a frequency range over which aconvective ridge is analyzed in determining a volumetric flow rate ofthe flow.

In one embodiment, constructing a plot of convection velocity of thecoherent structures as a function of frequency includes: constructingfrom the signals at least a portion of a k-ω plot; identifying aconvective ridge in the k-ω plot over a first frequency range;determining a first slope of the convective ridge, the first slope beingindicative of the nominal velocity of the flow; identifying a pluralityof portions of the convective ridge over a plurality of second frequencyranges, each second frequency range being smaller than the firstfrequency range and having a respective midpoint; determining a secondslope for each of the portions of the convective ridge, each secondslope being indicative of a nominal convection velocity of coherentstructures having a range of length scales corresponding to anassociated second frequency range; normalizing the nominal convectionvelocities of coherent structures using the nominal velocity of the flowto provide normalized convection velocities; and plotting eachnormalized convection velocity as a function of the respective midpointnon-dimensionalized by the nominal velocity of the flow and the diameterof the pipe to provide the plot. In this embodiment, the first frequencyrange may be adjusted based on the slope. For example, a non-dimensionallength scale that is least sensitive to stratification is used todetermine the mid-point of the first frequency range, where thenon-dimensional length scale that is least sensitive to stratificationis determined by comparing a plurality of dispersion plots for differentlevels of stratification and identifying the pivot point of thedispersion plots from one dispersion plot to another.

In another aspect of the invention, first and second spatial arrays eachhave at least two sensors disposed at different axial locations alongthe pipe. Each of the sensors in the first array provides a first signalindicative of unsteady pressure created by coherent structuresconvecting with a portion of the flow passing through an upper portionof the pipe, and each of the sensors in the second array provides asecond signal indicative of unsteady pressure created by coherentstructures convecting with a portion of the flow passing through a lowerportion of the pipe. A first velocity of the flow in the upper portionof the pipe is determined using the first signals, and a second velocityof the flow in the lower portion of the pipe is determined using thesecond signals. The first and second velocities are compared todetermine the parameter of the flow. The parameter of the flow mayinclude at least one of: level of stratification of the flow andvolumetric flow rate of the flow. The microprocessor may normalize thefirst and second velocities before comparing the first and secondvelocities. The first spatial array may be aligned axially along a topof the pipe and the second spatial array may be aligned axially along abottom of the pipe.

In one embodiment, at least one additional spatial array is alignedaxially along the pipe and positioned between the first and secondspatial arrays. Each of the sensors in the at least one additional arrayprovides a third signal indicative of unsteady pressure created bycoherent structures convecting with a portion of the flow proximate thesensor. For each additional spatial array, the signal processordetermines a third velocity of the flow near the additional spatialarray using the third signals. The signal processor compares the first,second, and third velocities to determine the parameter of the flow.

In yet another aspect of the invention, an apparatus for measuring aparameter of a flow passing through a pipe comprises a spatial array ofsensors disposed at different axial locations along the pipe, where eachof the sensors includes a pair of sensor half-portions disposed onopposing lateral surfaces of the pipe. Each pair of sensor half-portionsprovides a pressure signal indicative of unsteady pressure created bycoherent structures convecting with the flow within the pipe at acorresponding axial location of the pipe. A signal processor determinesa nominal velocity of the flow within the pipe using the signals.

In one embodiment, each sensor half-portion is formed by a piezoelectricfilm material. Each sensor half-portion may be coupled to a steel strapthat extends around and clamps onto the outer surface of the pipe.

In various aspects and embodiments described herein, the at least twopressure sensors may be selected from a group consisting of:piezoelectric, piezoresistive, strain gauge, strain-based sensor, PVDF,optical sensors, ported ac pressure sensors, accelerometers, velocitysensors, and displacement sensors. In various aspects and embodimentsdescribed herein, the sensors may be disposed on an outer surface of thepipe and do not contact the fluid.

The foregoing and other objects, and features of the present inventionwill become more apparent in light of the following detailed descriptionof exemplary embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawing wherein like items are numbered alike inthe various Figures:

FIG. 1 is schematic diagram of an apparatus for determining at least oneparameter associated with a stratified fluid flowing in a pipe.

FIG. 2 is a cross-sectional schematic view of non-stratified, turbulent,Newtonian flow through a pipe.

FIG. 3 is a block diagram of a flow logic used in the apparatus of thepresent invention.

FIG. 4 is a k-ω plot of data processed from an apparatus embodying thepresent invention that illustrates slope of the convective ridge, and aplot of the optimization function of the convective ridge.

FIG. 5 is a k-ω plot of data processed from an apparatus embodying thepresent invention that illustrates a non-linear ridge in the k-ω plot,as may be found with dispersive flow.

FIG. 6 is a flow chart depicting a method of quantifying the level ofstratification.

FIG. 7 depicts an example of a dispersion plot for a 30 inchhydrotransport line with a nominal velocity of 12 ft/sec created usingthe method of the present invention.

FIG. 8 depicts an example of a dispersion plot for a 27 inchhydrotransport line with a nominal velocity of 15 ft/sec created usingthe method of the present invention.

FIG. 9 depicts an example of a dispersion plot for a 10 inch, 1%consistency pulp-in-water suspension flowing at a nominal volumetricflow rate of 10 ft/sec created using the method of the presentinvention.

FIG. 10 depicts an example of a dispersion plot for a mixture ofbitumen, sand, water, and air at 25 ft/sec in a 4 inch diameter pipecreated using the method of the present invention.

FIG. 11 depicts an example of a dispersion plot for a 16 inch pipeflowing water at a nominal flow velocity of 10 ft/sec created using themethod of the present invention.

FIG. 12 depicts an example of a dispersion plot for a 24 inch tailingsline operating at 8 ft/sec created using the method of the presentinvention.

FIG. 13 is a plot depicting a flow rate determined by the method of thepresent invention demonstrated compared with a flow rate determined byan in-line magnetic flow meter.

FIG. 14 depicts a longitudinal cross-section of an alternativeembodiment of the present invention.

FIG. 15 depicts a transverse (radial) cross-section of the embodiment ofFIG. 14.

FIG. 16 depicts a plot of the normalized velocity for the top and bottomarrays in the embodiment of FIG. 14.

FIG. 17 depicts a transverse (radial) cross-section of the embodiment ofFIG. 14 including additional arrays of sensors.

FIG. 18 depicts a side elevation view of the embodiment of FIG. 14including additional arrays of sensors.

FIG. 19 depicts a plot of normalized velocity sensed by each array ofFIGS. 17 and 18.

FIG. 20 depicts a transverse (radial) cross-section of anotheralternative embodiment of the present invention.

FIG. 21 depicts a side elevation view of the alternative embodiment ofFIG. 20.

DETAILED DESCRIPTION

As described in commonly-owned U.S. Pat. No. 6,609,069 to Gysling,entitled “Method and Apparatus for Determining the Flow Velocity Withina Pipe”, and U.S. patent application Ser. No. 10/007,736, filed on Nov.11, 2001, which are incorporated herein by reference in their entirety,unsteady pressures along a pipe caused by coherent structures (e.g.,turbulent eddies and vortical disturbances) that convect with a fluidflowing in the pipe, contain useful information regarding parameters ofthe fluid. The present invention provides various means for using thisinformation to measure parameters of a stratified flow, such as, forexample, velocity, level/degree of stratification, and volumetric flowrate.

Referring to FIG. 1, an apparatus 10 for measuring at least oneparameter associated with a flow 13 flowing within a duct, conduit orother form of pipe 14, is shown. The parameter of the flow 13 mayinclude, for example, at least one of: velocity of the flow 13,volumetric flow rate of the flow 13, and level of stratification of theflow 13. In FIG. 1, the flow 13 is depicted as being stratified, where avelocity profile 122 of the flow 13 is skewed from the top of the pipe14 to the bottom of the pipe 14, as may be found in industrial fluidflow processes involving the transportation of a high mass fraction ofhigh density, solid materials through a pipe where the larger particlestravel more slowly at the bottom of the pipe. For example, the flow 13may be part of a hydrotransport process.

Referring to FIG. 2, the flow 13 is again shown passing through pipe 14.However, in FIG. 2, the flow 13 is depicted as a non-stratified,Newtonian flow operating in the turbulent regime at Reynolds numbersabove about 100,000. The flow 13 of FIG. 2, has a velocity profile 122that is uniformly developed from the top of the pipe 14 to the bottom ofthe pipe 14. Furthermore, the coherent structures 120 in thenon-stratified, turbulent, Newtonian flow 13 of FIG. 2 exhibit verylittle dispersion. In other words, the speed of convection of thecoherent structures 120 is not strongly dependent on the physical sizeof the structures 120. As used herein, dispersion describes thedependence of convection velocity with wavelength, or equivalently, withtemporal frequency. Flows for which all wavelengths convect at aconstant velocity are termed “non-dispersive”. For turbulent, Newtonianflow, there is typically not a significant amount of dispersion over awide range of wavelength to diameter ratios.

Sonar-based flow measurement devices, such as, for example, the devicedescribed in aforementioned U.S. Pat. No. 6,609,069 to Gysling, haveadvantageously applied the non-dispersive characteristic of turbulent,Newtonian flow in accurately determining flow rates. For stratifiedflows such as those depicted in FIG. 1, however, some degree ofdispersion is exhibited. In other words, the coherent structures 120convect at velocities that depend on their size, with larger lengthscale coherent structures 120 tending to travel slower than smallerlength scale structures 120. As a result, some of the underlyingassumptions associated with prior sonar-based flow measurement devices,namely that the speed of convection of the coherent structures 120 isnot strongly dependent on the physical size of the structures 120, areaffected by the presence of stratification.

The apparatus 10 of FIG. 1 accurately measures parameters such asvelocity, level of stratification, and volumetric flow rate of astratified flow 13. The apparatus 10 includes a spatial array 11 of atleast two sensors 15 disposed at different axial locations x₁ . . .x_(N) along the pipe 14. Each of the sensors 15 provides a pressuresignal P(t) indicative of unsteady pressure created by coherentstructures convecting with the flow 13 within the pipe 14 at acorresponding axial location x₁ . . . x_(N) of the pipe 14. The pressuregenerated by the convective pressure disturbances (e.g., eddies 120) maybe measured through strained-based sensors 15 and/or pressure sensors15. The sensors 15 provide analog pressure time-varying signals P₁(t),P₂(t), P₃(t) . . . P_(N)(t) to a signal processor 19, which determinesthe parameter of the flow 13 using pressure signals from the sensors 15,and outputs the parameter as a signal 21.

While the apparatus 10 is shown as including four sensors 15, it iscontemplated that the array 11 of sensors 15 includes two or moresensors 15, each providing a pressure signal P(t) indicative of unsteadypressure within the pipe 14 at a corresponding axial location X of thepipe 14. For example, the apparatus may include 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24 sensors15. Generally, the accuracy of the measurement improves as the number ofsensors 15 in the array 11 increases. The degree of accuracy provided bythe greater number of sensors 15 is offset by the increase in complexityand time for computing the desired output parameter of the flow.Therefore, the number of sensors 15 used is dependent at least on thedegree of accuracy desired and the desire update rate of the outputparameter provided by the apparatus 10.

The signals P₁(t) . . . P_(N)(t) provided by the sensors 15 in the array11 are processed by the signal processor 19, which may be part of alarger processing unit 20. For example, the signal processor 19 may be amicroprocessor and the processing unit 20 may be a personal computer orother general purpose computer. It is contemplated that the signalprocessor 19 may be any one or more analog or digital signal processingdevices for executing programmed instructions, such as one or moremicroprocessors or application specific integrated circuits (ASICS), andmay include memory for storing programmed instructions, set points,parameters, and for buffering or otherwise storing data.

The signal processor 19 may output the one or more parameters 21 to adisplay 24 or another input/output (I/O) device 26. The I/O device 26may also accepts user input parameters. The I/O device 26, display 24,and signal processor 19 unit may be mounted in a common housing, whichmay be attached to the array 11 by a flexible cable, wirelessconnection, or the like. The flexible cable may also be used to provideoperating power from the processing unit 20 to the array 11 ifnecessary.

To determine the one or more parameters 21 of the flow 13, the signalprocessor 19 applies the data from the sensors 15 to flow logic 36executed by signal processor 19. Referring to FIG. 3, an example of flowlogic 36 is shown. Some or all of the functions within the flow logic 36may be implemented in software (using a microprocessor or computer)and/or firmware, or may be implemented using analog and/or digitalhardware, having sufficient memory, interfaces, and capacity to performthe functions described herein.

The flow logic 36 includes a data acquisition unit 126 (e.g., A/Dconverter) that converts the analog signals P₁(t) . . . P_(N)(t) torespective digital signals and provides the digital signals P₁(t) . . .P_(N)(t) to FFT logic 128. The FFT logic 128 calculates the Fouriertransform of the digitized time-based input signals P₁(t) . . . P_(N)(t)and provides complex frequency domain (or frequency based) signalsP₁(ω), P₂(ω), P₃(ω), . . . P_(N)(ω) indicative of the frequency contentof the input signals. Instead of FFT's, any other technique forobtaining the frequency domain characteristics of the signalsP₁(t)-P_(N)(t), may be used. For example, the cross-spectral density andthe power spectral density may be used to form a frequency domaintransfer functions (or frequency response or ratios) discussedhereinafter.

One technique of determining the convection velocity of the coherentstructures (e.g., turbulent eddies) 120 within the flow 13 is bycharacterizing a convective ridge of the resulting unsteady pressuresusing an array of sensors or other beam forming techniques, similar tothat described in U.S. patent application Ser. No. 09/729,994, filedDec. 4, 2000, now U.S. Pat. No. 6,609,069, which is incorporated hereinby reference.

A data accumulator 130 accumulates the frequency signals P₁(ω)-P_(N)(ω)over a sampling interval, and provides the data to an array processor132, which performs a spatial-temporal (two-dimensional) transform ofthe sensor data, from the xt domain to the k-ω domain, and thencalculates the power in the k-ω plane, as represented by a k-ω plot.

The array processor 132 uses standard so-called beam forming, arrayprocessing, or adaptive array-processing algorithms, i.e. algorithms forprocessing the sensor signals using various delays and weighting tocreate suitable phase relationships between the signals provided by thedifferent sensors, thereby creating phased antenna array functionality.In other words, the beam forming or array processing algorithmstransform the time domain signals from the sensor array into theirspatial and temporal frequency components, i.e. into a set of wavenumbers given by k=2π/λ where λ is the wavelength of a spectralcomponent, and corresponding angular frequencies given by ω=2πν.

The prior art teaches many algorithms of use in spatially and temporallydecomposing a signal from a phased array of sensors, and the presentinvention is not restricted to any particular algorithm. One particularadaptive array processing algorithm is the Capon method/algorithm. Whilethe Capon method is described as one method, the present inventioncontemplates the use of other adaptive array processing algorithms, suchas MUSIC algorithm. The present invention recognizes that suchtechniques can be used to determine flow rate, i.e. that the signalscaused by a stochastic parameter convecting with a flow are timestationary and have a coherence length long enough that it is practicalto locate sensors 15 apart from each other and yet still be within thecoherence length.

Convective characteristics or parameters have a dispersion relationshipthat can be approximated by the straight-line equation,k=ω/u,

-   -   where u is the convection velocity (flow velocity). A plot of        k-ω pairs obtained from a spectral analysis of sensor samples        associated with convective parameters portrayed so that the        energy of the disturbance spectrally corresponding to pairings        that might be described as a substantially straight ridge, a        ridge that in turbulent boundary layer theory is called a        convective ridge. As will be described hereinafter, as the flow        becomes increasingly dispersive, the convective ridge becomes        increasingly non-linear. What is being sensed are not discrete        events of coherent structures 120, but rather a continuum of        possibly overlapping events forming a temporally stationary,        essentially white process over the frequency range of interest.        In other words, the convective coherent structures 120 are        distributed over a range of length scales and hence temporal        frequencies.

To calculate the power in the k-ω plane, as represented by a k-ω plot(see FIG. 4) of either the signals, the array processor 132 determinesthe wavelength and so the (spatial) wavenumber k, and also the(temporal) frequency and so the angular frequency w, of various of thespectral components of the stochastic parameter. There are numerousalgorithms available in the public domain to perform thespatial/temporal decomposition of arrays of sensors 15.

The present embodiment may use temporal and spatial filtering toprecondition the signals to effectively filter out the common modecharacteristics Pcommon mode and other long wavelength (compared to thesensor spacing) characteristics in the pipe 14 by differencing adjacentsensors 15 and retain a substantial portion of the stochastic parameterassociated with the flow field and any other short wavelength (comparedto the sensor spacing) low frequency stochastic parameters.

In the case of suitable coherent structures 120 being present, the powerin the k-ω plane shown in a k-ω plot of FIG. 4 shows a convective ridge124. The convective ridge represents the concentration of a stochasticparameter that convects with the flow and is a mathematicalmanifestation of the relationship between the spatial variations andtemporal variations described above. Such a plot will indicate atendency for k-ω pairs to appear more or less along a line 124 with someslope, the slope indicating the flow velocity.

Once the power in the k-ω plane is determined, a convective ridgeidentifier 134 uses one or another feature extraction method todetermine the location and orientation (slope) of any convective ridge124 present in the k-ω plane. In one embodiment, a so-called slantstacking method is used, a method in which the accumulated frequency ofk-ω pairs in the k-ω plot along different rays emanating from the originare compared, each different ray being associated with a different trialconvection velocity (in that the slope of a ray is assumed to be theflow velocity or correlated to the flow velocity in a known way). Theconvective ridge identifier 134 provides information about the differenttrial convection velocities, information referred to generally asconvective ridge information.

The analyzer 136 examines the convective ridge information including theconvective ridge orientation (slope). Assuming the straight-linedispersion relation given by k=ω/u, the analyzer 136 determines the flowvelocity and/or volumetric flow, which are output as parameters 21. Thevolumetric flow is determined by multiplying the cross-sectional area ofthe inside of the pipe with the velocity of the process flow.

As previously noted, for turbulent, Newtonian fluids, there is typicallynot a significant amount of dispersion over a wide range of wavelengthto diameter ratios. As a result, the convective ridge 124 in the k-ωplot is substantially straight over a wide frequency range and,accordingly, there is a wide frequency range for which the straight-linedispersion relation given by k=ω/u provides accurate flow velocitymeasurements.

For stratified flows, however, some degree of dispersion exists suchthat coherent structures 120 convect at velocities which depend on theirsize. As a result of increasing levels of dispersion, the convectiveridge 124 in the k-ω plot becomes increasingly non-linear. For example,FIG. 5 depicts a k-ω plot having a non-linear ridge 124, which is shownhaving an exaggerated curvature for purposes of description. Thus,unlike the non-dispersive flows, determining the flow rate of adispersive mixture by tracking the speed at which coherent structures120 convect requires a methodology that accounts for the presence ofsignificant dispersion.

Referring to FIGS. 3, 5, and 6, a method can be described forquantifying the level of stratification, as well as to measure thevolumetric flow rate, in stratified flows. The method, generallyindicated in FIG. 6 at 60, begins with block 62, where a velocity U₁ ofthe flow 13 is initialized. Initially, the velocity U₁ may be selected,for example, based on operating experience, expected velocities, and thelike.

Next, in block 64, maximum and minimum frequencies (F_(max) and F_(min))defining a first frequency range ΔF₁ are determined using the velocityU₁, the pipe diameter D, and maximum and minimum non-dimensional lengthscales FD/U. As will be discussed hereinafter, the maximum and minimumnon-dimensional length scales may be determined using a calibrationroutine wherein the maximum and minimum non-dimensional length scalesare selected to define a range centered on a non-dimensional lengthscale that is least sensitive to stratification. In the example shown inFIG. 5, a maximum non-dimensional length scale of FD/U=2.33 and aminimum non-dimensional length scale of FD/U=0.66 are used. Thus, forthis example:F _(max)=2.33*U ₁ /DF _(min)=0.66*U ₁ /DIt will be appreciated, however, that different non-dimensional lengthscales may be used, depending on the results of the calibration routine.

The method continues at block 66, where the convective ridge identifier134 identifies a convective ridge 124 in the k-ω plot as a straight line123 (FIG. 5) over the first frequency range ΔF₁. In block 66, theconvective ridge identifier 134 determines the slope of the straightline representation of the first convective ridge (e.g., the slope ofline 123), and, using this slope, the analyzer 136 determines a nominalvelocity U₂ (block 68). Recalling that FD/U is the inverse of λ/D, whereλ is wavelength, the non-dimensional length scale of FD/U ranging from0.66 to 2.33 corresponds to 1/D's (for λ=1) of 1.5 to 0.43. Note thatthe nominal velocity U₂ is centered on coherent structures with lengthscales of 0.667 diameters in length.

After the nominal velocity U₂ is calculated over the frequency range ΔF₁in block 68, the nominal velocity U₂ is compared to the velocity U₁ inblock 70 and, if the two velocities are equal (or approximately equalwithin an appropriate range), then the nominal velocity U₂ is providedas the nominal velocity U of the flow 13 (block 72), which may be usedto determine volumetric flow rate of the flow 13.

If, however, the velocities U₁ and U₂ are not equal (or not within theappropriate range) in block 70, U₁ is set equal to U₂ (block 74) and theprocess returns to block 64 where the maximum and minimum frequencies(F_(max) and F_(min)) defining the first frequency range ΔF₁ aredetermined using the new velocity U₁. This iterative process continuesuntil U₁=U₂ at block 70.

After the nominal velocity U of the flow 13 is determined (block 72),average convection velocities are then calculated over a plurality ofrelatively small frequency ranges ΔF₂. In method 60, this isaccomplished by identifying a plurality of portions 125 (FIG. 5) of theconvective ridge 124 over a plurality of second frequency ranges ΔF₂(block 76), where each second frequency range ΔF₂ is smaller than thefirst frequency range AF, and has a unique midpoint frequency, as shownat 127 in FIG. 5. The convective ridge identifier 134 then determines aslope of each portion 125 of the convective ridge 124 as a best fit lineforced to fit through the origin and the portion of the convective ridge(block 78). Using the slope of each portion 125, the analyzer 136determines a nominal convection velocity of coherent structures having arange of length scales corresponding to the associated second frequencyrange ΔF₂ (block 80). Next, in block 82, the analyzer 136 normalizesthese nominal convection velocities using the nominal velocity U, andthen plots each normalized convection velocity as a function of therespective midpoint frequency 127 (non-dimensionalized by the nominalvelocity U and the diameter D of the pipe) to create a dispersion plot(block 84).

The functional dependency of the velocity versus frequency is capturedby a linear fit (block 86). For non-dispersive flows, the linear fitwould have a slope of 0.0 and a y-intercept of 1.0. Any variation tothis can be attributed to dispersion. For flows with dispersion, theslope of the linear fit serves as a quantifiable measure of thestratification (block 88).

FIG. 7 depicts an example of a dispersion plot for a 30 inchhydrotransport line with a nominal velocity U of 12 ft/sec. createdusing the method of the present invention. For the example given in FIG.7, the dispersion metric, i.e., the slope of the dispersion plot, is19%, which indicates a significant amount of dispersion. The convectionvelocity, determined as described above for wavelengths of one diameteris 0.8 of the velocity of the wavelength with a length of 0.667diameters (i.e., FD/U=1.5). Structures with wavelengths centered around¼ diameters (i.e., FD/U=4) are shown to be convecting roughly 1.4 timesthe convection velocity of wavelengths centered around 0.667 diameters.

The dispersion plot can also be used as part of a calibration procedureto accurately determine the volumetric flow rate in the presence ofstratification. For example, the range of non-dimensional length scalesof FD/U used in determining the nominal flow velocity U may be selectedas that range which is least sensitive to stratification. This may beaccomplished, for example, by creating two or more dispersion plots,each at a different level of stratification. For example, in thehydrotransport of solids, dispersion plots may be created for differentconcentrations of solids. It has been determined that, as the slope ofthe linear fit of the dispersion plot increases from one level ofstratification to another, the point about which the linear fit pivotsprovides a good approximation of the non-dimensional length scale FD/Uthat is least sensitive to stratification. Thus, the non-dimensionallength scale FD/U that is least sensitive to stratification can beapproximated by comparing the dispersion plots for different levels ofstratification and identifying the pivot point of the linear fit of thedispersion plot from one dispersion plot to another. The non-dimensionallength scale FD/U associated with the pivot point can be used as themid-point for the range of non-dimensional length scales of FD/U used inmethod 60 of FIG. 6 for determining the nominal flow velocity U and thedispersion plot.

FIGS. 7-12 depict various examples of dispersion plots created using themethod of the present invention. In each of these examples, a spatialwave number (i.e., FD/U) range of 0.66 to 2.33 with a center wave numberof 1.5 was used. FIG. 8 shows an example of a hydrotransport of bitumen,sand, water, and air. In this case, the flow is in a 27 inch pipe,traveling at a nominal flow rate of 15 ft/sec. Here the slope of thedispersion plot is calculated to be 0.078 (i.e., a dispersion parameterof 7.8%).

FIG. 9 shows a dispersion plot for a 10 inch, 1% consistencypulp-in-water suspension flowing at a nominal volumetric flow rate of 10ft/sec. The resulting linear curve fit equation, shown in FIG. 9, has aslope of −0.023, which can be classified as non-dispersive flow.

FIG. 10 shows a dispersion plot for a mixture of bitumen, sand, water,and air at 25 ft/sec in a 4 inch diameter pipe. The resulting linearcurve fit equation, shown in FIG. 10, has a slope of −0.003, which canbe classified as non-dispersive flow.

FIG. 11 shows a dispersion plot for a 16 inch pipe flowing water at anominal flow velocity of 10 ft/sec. The resulting linear curve fitequation, shown in FIG. 11, has a slope of −0.013, which can beclassified as non-dispersive flow.

FIG. 12 shows the dispersion characteristics for a 24 inch tailings lineoperating at 8 ft/sec. As shown, the tailings line is exhibiting adispersion metric of about 18%. Using a spatial wave number (i.e. FD/U)range of 0.66 to 2.33 with a center wave number of 1.5, the velocitydetermined by the method of the present invention demonstrated goodagreement with an in-line magnetic flow meter, as demonstrated in FIG.13. Centering the frequency range on structure with a length scale of ⅔the pipe diameter seems reasonable and consistent with conceptual model.Although accurate reference data from other stratified flows iscurrently not available, the similar dispersion characteristics suggestthat using this, or similar, non-dimensional length scales should be areasonable approach for interpreting the volumetric flow rates otherstratified flows using sonar-based flow measurement.

Comparison of the examples provided in FIGS. 7-12 reveals that the slopeof the dispersion curve tracks, at least qualitatively, the level ofstratification present. The slope approaches zero for well-mixedslurries and Newtonian fluids and increases with decreasing flow rates,consistent with stratification increasing with decreasing flow rates.

FIG. 14 depicts a longitudinal cross-section of an apparatus 100 fordetermining the level of stratification of the flow 13 in accordancewith an alternative embodiment of the present invention, and FIG. 15depicts a transverse (radial) cross-section of the apparatus 100. Inthis embodiment, the apparatus 100 determines the level ofstratification of the flow 13 and a volumetric flow rate of the flow 13by comparing locally measured velocities at the top and bottom of thepipe 14. The apparatus 100 includes a first spatial array 11 of at leasttwo sensors 15 disposed at different axial locations x₁ . . . x_(N)along the top of the pipe 14. Each of the sensors 15 provides a pressuresignal P(t) indicative of unsteady pressure created by coherentstructures 120 convecting with a portion of the flow 13 near the top ofthe pipe 14. The apparatus further includes a second spatial array 11′of at least two sensors 15 disposed at the different axial locations x₁. . . x_(N) along the bottom of the pipe 14. Each of the sensors 15 inthe second spatial array 11′ provides a pressure signal P(t)′ indicativeof unsteady pressure created by coherent structures 120 convecting witha portion of the flow 13 near the bottom of the pipe 14.

The sensors 15 from each array 11 and 11′ provide analog pressuretime-varying signals P₁(t), P₂(t), P₃(t) . . . P_(N)(t) to one or moresignal processors 19 to determine flow velocity of each array. Thesignal processor 19 applies the pressure signals from the sensors 15 inthe array 11 to flow logic 36 executed by the signal processor 19 todetermine the velocity of the flow 13 near the top of the pipe 14. Thesignal processor 19 applies the pressure signals from the sensors 15 inthe array 11′ to flow logic 36 executed by the signal processor 19 todetermine the velocity of the flow 13 near the bottom of the pipe 14.The flow logic 36 applies a sonar array-processing algorithm asdescribed above with respect to FIGS. 3 and 4 to determine thevelocities.

In the embodiment shown, each of the sensors 15 is formed by a strip ofpiezoelectric material such as, for example, the polymer, polarizedfluoropolymer, PVDF, which measures the strain induced within the pipe14 due to the coherent structures convecting with the flow 13. Thesensors 15 can be formed from PVDF films, co-polymer films, or flexiblePZT sensors, similar to that described in “Piezo Film Sensors technicalManual” provided by Measurement Specialties, Inc. of Fairfield, N.J.,which is incorporated herein by reference. The strips of piezoelectricfilm material forming the sensors 15 along each axial location x₁ . . .x_(N) of the pipe 14 may be adhered to the surface of a steel strap 206(e.g., a hose clamp) that extends around and clamps onto the outersurface of the pipe 14. As discussed hereinafter, other types of sensors15 and other methods of attaching the sensors 15 to the pipe 14 may beused.

In the embodiment shown, the sensors 15 extend over an arcuate outersurface of the pipe 14 defined by the angle θ, which is centered on avertical line 203. For example, the each of the sensors 15 may extendabout ¼ of the circumference of the pipe 14. Because the sensors 15 donot extend across the side surfaces of the pipe 14, and because thesensors 15 tend to sense local disturbances within the flow 13, thesensors 15 sense coherent structures 120 convecting with a portion ofthe flow 13 near the top or bottom of the pipe 14. Accordingly, as thesize of the sensors 15 are decreased (i.e., as the angle θ isdecreased), the unsteady pressures sensed by the by the sensors 15 moreaccurately indicate the nominal flow velocity of the portion of the flow13 near the top or bottom of the pipe 14. However, the degree ofaccuracy provided by decreasing the size of the sensors is offset by thedecrease in signal strength provided by the sensors 15. Therefore, thesize of the sensors 15 (i.e., the angle θ used) is dependent at least onthe degree of accuracy desired and the strength of the signals P₁(t),P₂(t), P₃(t) . . . P_(N)(t) required by the signal processor 19.

While the apparatus 100 is shown as including four sensors 15 in eacharray 11 and 11′, it is contemplated that each array 11 and 11′ mayinclude two or more sensors 15, with each sensor 15 providing a pressuresignal P(t) indicative of unsteady pressure within the pipe 14 at acorresponding axial location X of the pipe 14. For example, theapparatus may include 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,16, 17, 18, 19, 20, 21, 22, 23, or 24 sensors 15. Generally, theaccuracy of the measurement improves as the number of sensors 15 in thearrays 11 and 11′ increases. The degree of accuracy provided by thegreater number of sensors 15 is offset by the increase in complexity andtime for computing the desired output parameter of the flow. Therefore,the number of sensors 15 used is dependent at least on the degree ofaccuracy desired and the desire update rate of the output parameterprovided by the apparatus 100.

FIG. 16 depicts a plot of the normalized velocity for the top and bottomarrays 11 and 11′. The ratio of the velocities near the top and bottomof the pipe 14 correlates to the level of stratification of the flow 13.Under conditions where there is no stratification, flow near the top andbottom of the pipe (and the coherent structures convecting with theflow) will travel at approximately the same velocity. As the level ofstratification increases, the top array 11 will measure a highernormalized velocity and the bottom array 11′ will measure a lowernormalized velocity. Thus, by comparing the velocities near the top andbottom of the pipe 14, the level of stratification of the flow 13 can bedetermined.

The velocities near the top and bottom of the pipe 14 can also be usedto estimate the nominal velocity of the flow 13, which, in turn, may beused to determine the volumetric flow rate of the flow 13. For example,nominal velocity may be determined using an average of the twovelocities or some other ratio of the two velocities, wherein the ratiois dependent on the level of stratification (or difference between thetwo velocities). In another example, as shown in FIG. 16, the velocitiesnear the top and bottom of the pipe may be plot as a function of thedistance between the top and bottom arrays. In this example, thedistance between the top and bottom arrays is approximately equal to thepipe diameter, and each increment on the x-axis represents some portionof this distance. The velocities at the top and bottom of the pipedefine a straight line 210, which has a slope that changes with thelevel of stratification. Using this straight line, the velocities atdifferent distances between the top and bottom of the pipe can beestimated, and the velocity at the appropriate pipe location can be usedas the nominal velocity. In the example shown, velocity at the center ofthe pipe (mid-way between the top and bottom arrays) is estimated.

FIG. 17 depicts a transverse (radial) cross-section of the apparatus 100of FIG. 15, further including at least one additional spatial array 11″of sensors 15 aligned axially along the pipe 14 and being positionedbetween the first and second spatial arrays 11 and 11′. FIG. 18 depictsa side elevation view of this embodiment. The sensors 15 in eachadditional array 11″ provide analog pressure time-varying signals P₁(t),P₂(t), P₃(t) . . . P_(N)(t) to one or more signal processors 19, whichdetermines flow velocity of the fluid proximate each additional array11″. Optionally, each array 11″ may comprise a pair of sensors 15disposed on the pipe at a corresponding level between the top and bottomarrays 11 and 11′, as indicated at 215, 216, and 217. These optionalsensors 15 are shown in phantom in FIG. 17. For each array, the signalsoutput from the pair of sensors 15 at corresponding axial locations x₁ .. . . x_(N) are combined (e.g., summed) as a single input to the signalprocessor 19 to eliminate portions of the signal caused by horizontalbending modes of the pipe 14.

FIG. 19 depicts a plot of the normalized velocity for each array 11,11′, and 11″. As in the example of FIG. 16, the ratio of the velocitiesnear the top and bottom of the pipe 14 correlates to the level ofstratification of the flow 13. The additional arrays 11″ allow avelocity profile to be constructed, with the number of data points inthe profile being equal to the number of arrays 11, 11′ and 11″.Comparing the velocity profiles of FIG. 16 and FIG. 19, it can be seenthat the additional arrays 11″ used to create the profile of FIG. 19allow for a more accurate representation of the velocities at differentlocations in the pipe 14 than the straight line approximation of FIG.16.

As can be seen in the velocity profile of FIG. 19, the extreme top andbottom velocity readings (the velocity readings at arrays 1 and 7,respectively) tend to be the most diverse, with the reading at thetransverse sides of the pipe 14 (the reading at array 4) providing anominal velocity for the entire profile. Accordingly, it can be seenthat for measuring nominal velocity in stratified flow using an array ofsensors, it may be advantageous to sense unsteady pressures along thetransverse sides of the pipe, such that the areas of extreme diversityin velocity (i.e., the top and bottom of the pipe) are ignored. Forexample, the center-most array (array 4) may be used to determine thenominal velocity of the flow 13, or the center-most arrays (e.g., arrays3, 4, and 5) can be used to determine the nominal velocity of the flow.The present invention also contemplates that any array offset from thecenter horizontal array (i.e., array 4), such as arrays 3 and 5 orcombinations of other arrays (e.g., arrays 2 & 3 or arrays 5 & 6) may beused to determine the nominal or average velocity of the process flow13. The determination of which array or set of arrays to determine thenominal velocity is dependent on the level of stratification.

FIG. 20 depicts a transverse (radial) cross-section of an apparatus 200for determining the level of stratification of the flow 13 in accordancewith another alternative embodiment of the present invention, and FIG.21 depicts a side elevation view of the alternative embodiment of FIG.20. In this embodiment, the apparatus 10 includes a spatial array 11 ofat least two sensors 15 disposed at different axial locations x₁ . . .x_(N) along the pipe 14. Each of the sensors 15 includes a pair ofsensor half-portions 202 disposed on opposing lateral surfaces of thepipe 14. Each pair of sensor half-portions 202 provides a pressuresignal P(t) indicative of unsteady pressure created by coherentstructures 120 (FIG. 1) convecting with the flow 13 within the pipe 14at a corresponding axial location x₁ . . . x_(N) of the pipe 14. Thesensors 15 provide analog pressure time-varying signals P₁(t), P₂(t),P₃(t) . . . P_(N)(t) to a signal processor 19, which determines theparameter of the flow 13 using pressure signals from the sensors 15, andoutputs the parameter as a signal 21. The signals provided bycorresponding sensor half-pairs 202 in each sensor 15 may be combined(e.g., summed) as a single input to the signal processor 19, thuseliminating portions of the signal caused by horizontal bending modes ofthe pipe 14.

In the present embodiment, the sensor half-portions 202 areadvantageously placed on the lateral side surfaces of the pipe 14. Thesensor half-portions 202 extend over an arcuate outer surface of thepipe 14 defined by the angle θ, which is centered on a horizontal line204. For example, the each of the sensors 15 may extend about ¼ of thecircumference of the pipe 14. Because the sensor half-portions 202 donot extend across the top and bottom surfaces of the pipe 14, andbecause the sensor half-portions 202 tend to sense local disturbanceswithin the flow 13, the extreme regions of the velocity profile areignored. Accordingly, as the length of the sensor half-portions 202 isdecreased (i.e., as the angle θ is decreased), the unsteady pressuressensed by the sensor half-portions 202 provide a more localized velocitymeasurement and in some instances a more accurate indication of thenominal flow velocity for stratified flow. However, the degree ofaccuracy provided by decreasing the size of the sensor half-portions 202is offset by the decrease in signal strength provided by the sensor halfportions 202. Therefore, the size of the sensor half-portions 202 (i.e.,the angle θ used) is dependent at least on the degree of accuracydesired and the strength of the signals P₁(t), P₂(t), P₃(t) . . .P_(N)(t) required by the signal processor 19.

While the sensor portions 202 are centered about the horizontal plane ofthe pipe, it may be advantageous to dispose the sensor portions 202above or below the horizontal center of the pipe depending on theexpected level of stratification.

While the apparatus 10 is shown as including four sensors 15, it iscontemplated that the array 11 of sensors 15 includes two or moresensors 15, each providing a pressure signal P(t) indicative of unsteadypressure within the pipe 14 at a corresponding axial location X of thepipe 14. For example, the apparatus may include 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24 sensors15. Generally, the accuracy of the measurement improves as the number ofsensors in the array increases. The degree of accuracy provided by thegreater number of sensors is offset by the increase in complexity andtime for computing the desired output parameter of the flow. Therefore,the number of sensors used is dependent at least on the degree ofaccuracy desired and the desired update rate of the output parameterprovided by the apparatus 10.

The signals P₁(t) . . . P_(N)(t) provided by the sensors 15 in the array11 are processed by the signal processor 19, which may be part of alarger processing unit 20. For example, the signal processor 19 may be amicroprocessor and the processing unit 20 may be a personal computer orother general purpose computer. It is contemplated that the signalprocessor 19 may be any one or more analog or digital signal processingdevices for executing programmed instructions, such as one or moremicroprocessors or application specific integrated circuits (ASICS), andmay include memory for storing programmed instructions, set points,parameters, and for buffering or otherwise storing data.

To determine the one or more parameters 21 of the flow 13, the signalprocessor 19 applies the data from the sensors 15 to flow logic 36executed by signal processor 19. The flow logic 36 applies a sonararray-processing algorithm as described above with respect to FIGS. 3and 4 to determine the velocities. Some or all of the functions withinthe flow logic 36 may be implemented in software (using a microprocessoror computer) and/or firmware, or may be implemented using analog and/ordigital hardware, having sufficient memory, interfaces, and capacity toperform the functions described herein.

In the embodiment shown, each of the sensor half-portions 202 is formedby a piezoelectric material such as, for example, the polymer, polarizedfluoropolymer, PVDF, which measures the strain induced within the pipe14 due to the coherent structures convecting with the flow 13. Thesensor half-portions 202 can be formed from PVDF films, co-polymerfilms, or flexible PZT sensors, similar to that described in “Piezo FilmSensors technical Manual” provided by Measurement Specialties, Inc. ofFairfield, N.J., which is incorporated herein by reference. The PVDFmaterial forming each sensor half-portion 202 may be adhered to thesurface of a steel strap 206 (e.g., a hose clamp) that extends aroundand clamps onto the outer surface of the pipe 14. It is alsocontemplated that other methods of attaching the sensor half-portions202 to the pipe 14 may be used. For example, the sensor half-portions202 may be adhered directly to the pipe 14. As discussed hereinafter,other types of sensors 15 and other methods of attaching the sensors 15to the pipe 14 may be used.

As previously noted, as the size of the sensor half-portions 202 isdecreased (i.e., as the angle θ is decreased), the unsteady pressuressensed by the by the sensor half-portions 202 more accurately indicatethe nominal flow velocity for stratified flow. However, the degree ofaccuracy provided by decreasing the size of the sensor half-portions 202is offset by the decrease in signal strength provided by the sensor halfportions 202. Moreover, as the flow 13 becomes less stratified, it isadvantageous to increase the size of sensors 15 in order to sense alarger portion of the flow 13. Combining the teachings of FIGS. 14-21,yet another embodiment of the present invention can be described whereinthe size of the sensor half-portions 202 is increased or decreaseddepending on the level of stratification of the flow 13. This embodimentemploys a sensor arrangement similar to that shown in FIGS. 17 and 18,wherein a plurality of sensors 15 are disposed around the perimeter ofthe pipe 14 at each axial location x₁ . . . x_(N) of the pipe 14(including the optional sensors 15 shown in FIG. 17). For example, thesensors 15 along each axial location x₁ . . . x_(N) of the pipe 14 maycomprise strips of piezoelectric film material adhered to the surface ofa steel strap 206 (e.g., a hose clamp) that extends around and clampsonto the outer surface of the pipe 14. As discussed hereinafter, othertypes of sensors 15 and other methods of attaching the sensors 15 to thepipe 14 may be used.

In this embodiment, the sensors 15 arrays 11 and 11′ are used aspreviously described with reference to FIGS. 14-19. That is, the signalprocessor 19 applies the pressure signals from the sensors 15 in thearray 11 to flow logic 36 executed by the signal processor 19 todetermine the velocity of the flow 13 near the top of the pipe 14, andthe signal processor 19 applies the pressure signals from the sensors 15in the array 11′ to flow logic 36 executed by the signal processor 19 todetermine the velocity of the flow 13 near the bottom of the pipe 14.The signal processor 19 then compares the velocities near the top andbottom of the pipe 14 to determine the level of stratification of theflow 13.

Also in this embodiment, as shown in FIGS. 17 and 18, for each axiallocation x₁ . . . . x_(N) of the pipe 14 (e.g., for each strap 206), thesensors 15 positioned on one side of the pipe (e.g., the sensors 15 tothe left of vertical line 203) represent one sensor half-portion, andthe sensors 15 positioned on the opposite side of the pipe (e.g. thesensors 15 to the right of vertical line 203) represent the other sensorhalf portion. For each axial location x₁ . . . x_(N), the output signalsfrom each of the sensors 15 forming the sensor half portions arecombined (e.g., summed) and processed to determine the nominal velocityof the flow 13 as described with reference to FIGS. 20 and 21.

In response to the determined level of stratification, the signalprocessor 19 can adjust the size of the sensor half-portions byselecting the number of sensors 15 in each sensor half portion. Forexample, if a the level of stratification is high (e.g., there is alarge spread between the velocities at the top and bottom of the pipe14), the signal processor 19 may process only the signals from one pairof sensors 15. (e.g., the center-most sensors 15 located at line 216 ofFIG. 17) for each axial location x₁ . . . x_(N) to determine the nominalvelocity of the flow 13. If the level of stratification decreases (e.g.,there is a reduction in the spread between the velocities at the top andbottom of the pipe 14), the signal processor 19 may combine the signalsfrom an increased number of sensors 15 at each axial location x₁ . . .x_(N) (e.g., the sensors 15 located at lines 215, 216, and 217 of FIG.17) to determine the nominal velocity of the flow 13. Furthermore, ifthere is no stratification detected, the signal processor may combinethe signals from all of the sensors 15 at each axial location x₁ . . .x_(N) to determine the nominal velocity of the flow 13.

As discussed hereinbefore referring to FIGS. 17-19, the presentinvention also contemplates that any array offset from the centerhorizontal array (i.e., array 4), such as arrays 3 and 5 or combinationsof other arrays (e.g., arrays 2 & 3 or arrays 5 & 6) may be used todetermine the nominal or average velocity of the process flow 13. Thedetermination of which array or set of arrays to determine the nominalvelocity is dependent on the level of stratification. It is furthercontemplated that the selected arrays to determine the nominal velocityand volumetric flow of the process fluid may be dynamic selected inresponse to the measured level of stratification.

In any of the embodiments described herein, the sensors 15 may includeelectrical strain gages, optical fibers and/or gratings, ported sensors,ultrasonic sensors, among others as described herein, and may beattached to the pipe by adhesive, glue, epoxy, tape or other suitableattachment means to ensure suitable contact between the sensor and thepipe 14. The sensors 15 may alternatively be removable or permanentlyattached via known mechanical techniques such as mechanical fastener,spring loaded, clamped, clam shell arrangement, strapping or otherequivalents. Alternatively, strain gages, including optical fibersand/or gratings, may be embedded in a composite pipe 14. If desired, forcertain applications, gratings may be detached from (or strain oracoustically isolated from) the pipe 14 if desired. It is alsocontemplated that any other strain sensing technique may be used tomeasure the variations in strain in the pipe 14, such as highlysensitive piezoelectric, electronic or electric, strain gages attachedto or embedded in the pipe 14.

In various embodiments of the present invention, a piezo-electronicpressure transducer may be used as one or more of the pressure sensorsand it may measure the unsteady (or dynamic or ac) pressure variationsinside the pipe 14 by measuring the pressure levels inside the pipe. Inone embodiment of the present invention, the sensors 14 comprisepressure sensors manufactured by PCB Piezotronics of Depew, N.Y. Forexample, in one pressure sensor there are integrated circuitpiezoelectric voltage mode-type sensors that feature built-inmicroelectronic amplifiers, and convert the high-impedance charge into alow-impedance voltage output. Specifically, a Model 106B manufactured byPCB Piezotronics is used which is a high sensitivity, accelerationcompensated integrated circuit piezoelectric quartz pressure sensorsuitable for measuring low pressure acoustic phenomena in hydraulic andpneumatic systems. It has the unique capability to measure smallpressure changes of less than 0.001 psi under high static conditions.The 106B has a 300 mV/psi sensitivity and a resolution of 91 dB (0.0001psi).

The sensors 15 may incorporate a built-in MOSFET microelectronicamplifier to convert the high-impedance charge output into alow-impedance voltage signal. The sensors 15 may be powered from aconstant-current source and can operate over long coaxial or ribboncable without signal degradation. The low-impedance voltage signal isnot affected by triboelectric cable noise or insulationresistance-degrading contaminants. Power to operate integrated circuitpiezoelectric sensors generally takes the form of a low-cost, 24 to 27VDC, 2 to 20 mA constant-current supply.

Most piezoelectric pressure sensors are constructed with eithercompression mode quartz crystals preloaded in a rigid housing, orunconstrained tourmaline crystals. These designs give the sensorsmicrosecond response times and resonant frequencies in the hundreds ofkHz, with minimal overshoot or ringing. Small diaphragm diameters ensurespatial resolution of narrow shock waves.

The output characteristic of piezoelectric pressure sensor systems isthat of an AC-coupled system, where repetitive signals decay until thereis an equal area above and below the original base line. As magnitudelevels of the monitored event fluctuate, the output remains stabilizedaround the base line with the positive and negative areas of the curveremaining equal.

Furthermore it is contemplated that each of the sensors 15 may include apiezoelectric sensor that provides a piezoelectric material to measurethe unsteady pressures of the flow 13. The piezoelectric material, suchas the polymer, polarized fluoropolymer, PVDF, measures the straininduced within the process pipe 14 due to unsteady pressure variationswithin the flow 13. Strain within the pipe 14 is transduced to an outputvoltage or current by the attached piezoelectric sensors 15.

The PVDF material forming each piezoelectric sensor 15 may be adhered tothe outer surface of a steel strap that extends around and clamps ontothe outer surface of the pipe 14. The piezoelectric sensing element istypically conformal to allow complete or nearly complete circumferentialmeasurement of induced strain. The sensors can be formed from PVDFfilms, co-polymer films, or flexible PZT sensors, similar to thatdescribed in “Piezo Film Sensors technical Manual” provided byMeasurement Specialties, Inc. of Fairfield, N.J., which is incorporatedherein by reference. The advantages of this technique are the following:

-   -   1. Non-intrusive flow rate measurements    -   2. Low cost    -   3. Measurement technique requires no excitation source. Ambient        flow noise is used as a source.    -   4. Flexible piezoelectric sensors can be mounted in a variety of        configurations to enhance signal detection schemes. These        configurations include a) co-located sensors, b) segmented        sensors with opposing polarity configurations, c) wide sensors        to enhance acoustic signal detection and minimize vortical noise        detection, d) tailored sensor geometries to minimize sensitivity        to pipe modes, e) differencing of sensors to eliminate acoustic        noise from vortical signals.    -   5. Higher Temperatures (140C) (co-polymers)

The present invention can be embodied in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. The present invention can also be embodied in the form ofcomputer program code containing instructions embodied in tangiblemedia, such as floppy diskettes, CD-ROMs, hard drives, or any othercomputer-readable storage medium, wherein, when the computer programcode is loaded into and executed by a computer, the computer becomes anapparatus for practicing the invention. The present invention can alsobe embodied in the form of computer program code, for example, whetherstored in a storage medium, loaded into and/or executed by a computer,or transmitted over some transmission medium, such as over electricalwiring or cabling, through fiber optics, or via electromagneticradiation, wherein, when the computer program code is loaded into andexecuted by a computer, the computer becomes an apparatus for practicingthe invention. When implemented on a general-purpose microprocessor, thecomputer program code segments configure the microprocessor to createspecific logic circuits.

It should be understood that any of the features, characteristics,alternatives or modifications described regarding a particularembodiment herein may also be applied, used, or incorporated with anyother embodiment described herein. In addition, it is contemplated that,while the embodiments described herein are useful for flow havingdispersive properties (e.g., stratified flow), the embodiments describedherein can also be used for homogeneous flow with no dispersiveproperties.

Although the invention has been described and illustrated with respectto exemplary embodiments thereof, the foregoing and various otheradditions and omissions may be made therein and thereto withoutdeparting from the spirit and scope of the present invention.

1. An apparatus for measuring a parameter of a flow passing through apipe, the apparatus comprising: a spatial array of sensors disposed atdifferent axial locations along the pipe, each of the sensors providinga signal indicative of unsteady pressure created by coherent structuresconvecting with the flow; and a signal processor configured to:determine, from the signals, convection velocities of coherentstructures having different length scales, and compare the convectionvelocities to determine a level of stratification of the flow.
 2. Theapparatus of claim 1, wherein, in comparing the convection velocities,the signal processor is configured to: construct a plot of theconvection velocities as a function of the length scales, and determinea slope of a best-fit line through the plot, the slope of the lineindicating the level of stratification of the flow.
 3. The apparatus ofclaim 2, wherein the plot is normalized by a nominal velocity of theflow and a diameter of the pipe.
 4. The apparatus of claim 2, whereinthe slope is used to calibrate the signal processor to determine thevolumetric flow rate of the flow.
 5. The apparatus of claim 4, whereinthe signal processor is configured to: construct from the signals atleast a portion of a k-ω plot; and determine a frequency range overwhich the signal processor analyzes a convective ridge in the k-ω plotfor determining the volumetric flow rate.
 6. The apparatus of claim 2,wherein, in constructing the plot of convection velocity of the coherentstructures as a function of frequency, the signal processor isconfigured to: construct from the signals at least a portion of a k-ωplot; identify a convective ridge in the k-ω plot over a first frequencyrange; determine a first slope of the convective ridge, the first slopebeing indicative of a nominal velocity of the flow; identify a pluralityof portions of the convective ridge over a plurality of second frequencyranges, each second frequency range being smaller than the firstfrequency range and having a respective midpoint; determine a secondslope for each of the portions of the convective ridge, each secondslope being indicative of a nominal convection velocity of coherentstructures having a range of length scales corresponding to anassociated second frequency range; normalize the nominal convectionvelocities of coherent structures using the nominal velocity of the flowto provide normalized convection velocities; and plot each normalizedconvection velocity as a function of the respective midpointnon-dimensionalized by the nominal velocity of the flow and the diameterof the pipe to provide the plot.
 7. The apparatus of claim 6, whereinthe first frequency range is adjusted based on the slope.
 8. Theapparatus of claim 6, wherein a non-dimensional length scale that isleast sensitive to stratification is used to determine the mid-point ofthe first frequency range, the non-dimensional length scale that isleast sensitive to stratification being determined by comparing aplurality of dispersion plots for different levels of stratification andidentifying the pivot point of the dispersion plots from one dispersionplot to another.
 9. An apparatus for measuring a parameter of a flowpassing through a pipe, the apparatus comprising: a first spatial arrayof at least two sensors disposed at different axial locations along thepipe, each of the sensors in the first array providing a first signalindicative of unsteady pressure created by coherent structuresconvecting with a portion of the flow passing through an upper portionof the pipe; a second spatial array of at least two sensors disposed atdifferent axial locations along the pipe, each of the sensors in thesecond array providing a second signal indicative of unsteady pressurecreated by coherent structures convecting with a portion of the flowpassing through a lower portion of the pipe; and at least one signalprocessor configured to: determine a first velocity of the flow passingthrough the upper portion of the pipe using the first signals, determinea second velocity of the flow passing through the lower portion of thepipe using the second signals, and compare the first and secondvelocities to determine the parameter of the flow.
 10. The apparatus ofclaim 9, wherein the parameter of the flow includes at least one of:level of stratification of the flow and volumetric flow rate of theflow.
 11. The apparatus of claim 9, wherein the microprocessornormalizes the first and second velocities before comparing the firstand second velocities.
 12. The apparatus of claim 9, wherein the firstspatial array is aligned axially along a top of the pipe and the secondspatial array is aligned axially along a bottom of the pipe.
 13. Theapparatus of claim 9, further comprising: at least one additionalspatial array of at least two sensors disposed at different axiallocations along the pipe, each of the sensors in the at least oneadditional array providing a third signal indicative of unsteadypressure created by coherent structures convecting with a portion of theflow proximate the sensor, the at least one additional spatial arraybeing aligned axially along the pipe and being positioned between thefirst and second spatial arrays; and wherein, for each additionalspatial array, the at least one signal processor is further configuredto: determine a third velocity of the flow near the additional spatialarray using the third signals, and compare the first, second, and thirdvelocities to determine the parameter of the flow.
 14. The apparatus ofclaim 13, wherein the comparison of the first, second, and thirdvelocities provides a velocity profile of the flow passing through thepipe.
 15. The apparatus of claim 13, wherein the parameter of the flowincludes at least one of: level of stratification of the flow andvolumetric flow rate of the flow.
 16. The apparatus of claim 13, whereinthe microprocessor normalizes the first, second, and third velocitiesbefore comparing the first, second, and third velocities.
 17. Theapparatus of claim 9, wherein the parameter of the flow includes a levelof stratification of the flow and wherein, in response to the level ofstratification of the flow, the microprocessor selects a number ofsensors for use in determining a mean velocity of the flow.
 18. Anapparatus for measuring a parameter of a flow passing through a pipe,the apparatus comprising: a spatial array of sensors disposed atdifferent axial locations along the pipe, each of the sensors comprisinga pair of sensor half-portions disposed on opposing lateral surfaces ofthe pipe, wherein each pair of sensor half-portions provides a pressuresignal indicative of unsteady pressure created by coherent structuresconvecting with the flow within the pipe at a corresponding axiallocation of the pipe; and a signal processor configured to determine anominal velocity of the flow within the pipe using the signals.
 19. Amethod for measuring a parameter of a flow passing through a pipe usinga spatial array of sensors disposed at different axial locations alongthe pipe, each of the sensors providing a signal indicative of unsteadypressure created by coherent structures convecting with the flow, themethod comprising: determining, from the signals, convection velocitiesof coherent structures having different length scales, and comparing theconvection velocities to determine a level of stratification of theflow.
 20. The method of claim 19, wherein comparing the convectionvelocities includes: constructing a plot of the convection velocities asa function of the length scales, and determining a slope of a best-fitline through the plot, the slope of the line indicating the level ofstratification of the flow.
 21. The method of claim 20, wherein the plotis normalized by a nominal velocity of the flow and a diameter of thepipe.
 22. The method of claim 20, further comprising: constructing fromthe signals at least a portion of a k-ω plot; and using the slope,determining a frequency range over which the signal processor analyzes aconvective ridge in the k-ω plot for determining the volumetric flowrate.
 23. The method of claim 20, wherein constructing the plot ofconvection velocity of the coherent structures as a function offrequency comprises: constructing from the signals at least a portion ofa k-ω plot; identifying a convective ridge in the k-ω plot over a firstfrequency range; determining a first slope of the convective ridge, thefirst slope being indicative of a nominal velocity of the flow;identifying a plurality of portions of the convective ridge over aplurality of second frequency ranges, each second frequency range beingsmaller than the first frequency range and having a respective midpoint;determining a second slope for each of the portions of the convectiveridge, each second slope being indicative of a nominal convectionvelocity of coherent structures having a range of length scalescorresponding to an associated second frequency range; normalizing thenominal convection velocities of coherent structures using the nominalvelocity of the flow to provide normalized convection velocities; andplotting each normalized convection velocity as a function of therespective midpoint non-dimensionalized by the nominal velocity of theflow and the diameter of the pipe to provide the plot.
 24. The method ofclaim 23, wherein the first frequency range is adjusted based on theslope.
 25. The method of claim 24, wherein a non-dimensional lengthscale that is least sensitive to stratification is used to determine themid-point of the first frequency range, the non-dimensional length scalethat is least sensitive to stratification being determined by comparinga plurality of dispersion plots for different levels of stratificationand identifying the pivot point of the dispersion plots from onedispersion plot to another.